Defining the molecular drivers and modulators of MATR3 proteinopathy implicated in amyotrophic lateral sclerosis and frontotemporal dementia

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Project Summary Matrin-3 (MATR3) is a ubiquitous RNA-binding protein which is predicted to be largely disordered. Mutations in MATR3 have been linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) and wild- type MATR3 aggregates have been observed in sporadic ALS. However, it is unclear how pathogenic mutations perturb MATR3 toxicity and solubility. Additionally, RNA-binding may modulate liquid-liquid phase separation of MATR3. Although MATR3 enters the phase separated nucleolus, it is unclear if MATR3 is a driver or client of phase separation. While MATR3 does not mislocalize to the cytoplasm like other ALS RNA-binding proteins, it may mislocalize within the nucleus. These findings have been confounded by the complexities of rodent and primary neuron systems, so it is crucial to develop simple models of MATR3 proteinopathy to understand the molecular drivers and modifiers of aggregation. The driving hypothesis of this proposal is that pathogenic mutations in combination with diminished RNA binding are drivers of MATR3 aggregation, mislocalization, and toxicity which are major contributors to ALS pathology. A multifaceted approach of yeast, pure protein biochemistry, and mammalian neuronal systems will be used to investigate the drivers of MATR3 toxicity. Each of these systems has key benefits which together will uncover the mechanistic drivers and modifiers of ALS/FTD pathogenesis. Preliminary data suggests that simple yeast and pure protein biochemistry systems can be used to elucidate the molecular drivers and modifiers of MATR3 toxicity and aggregation. Nuclear compartments occupied by MATR3 will be identified using proximity labeling in SH-SY5Y cells, and mislocalization of MATR3 upon perturbation will be assessed. Finally, whether the molecular drivers of MATR3 can elicit ALS pathology will be investigated in primary mouse neurons. Specifically, this proposal will address two aims: 1) Define the molecular determinants of MATR3 toxicity and aggregation and 2) Investigate MATR3 pathology and localization to nuclear compartments in neurons. These studies will provide new insights into the underpinnings of ALS/FTD. A mentoring team has been established that will ensure key training opportunities in biochemistry, liquid-liquid phase separation, and neuroscience, which will provide excellent preparation for an academic research career.